Due to high integration of memory devices such as Dynamic Random Access Memory (DRAM), a technology of reducing a size of a semiconductor device has been required. In order to improve the speed and integration of the semiconductor device, the design rule of the device is reduced to decrease a channel length of the semiconductor device such as a metal oxide semiconductor field effect transistor (MOSFET).
As the semiconductor device becomes smaller and highly-integrated, the design rule of the semiconductor device has been reduced. As a result, the channel length of the MOSFET may become short. The reduction of the channel length closes a gap between a source region and a drain region, not to control of a short channel effect (SCE). A voltage of the drain region affects voltages of the source region and the channel region, which may result in degradation of active switch elements. The narrow gap between the source region and the drain region causes a punch-through phenomenon between the source region and the drain region. In order to prevent the punch-through phenomenon, a gate electrode for recessing and filling the inside of the semiconductor device is formed to increase an effective channel length, which is called a recess field effect transistor (FET) structure.
As the design rule of the device is reduced because the semiconductor device becomes smaller and highly-integrated, a size of a landing plug for electrically connecting a storage node to a bit line is decreased. The decrease of the size of the landing plug reduces an area contacted with a semiconductor substrate which is a junction region, thereby increasing a contact resistance. For example, a contact resistance is in inverse proportion to the contact area, and in proportion to the contact length. As a result, the decrease of the contact area increases the contact resistance. The decrease of the contact area increases an interface resistance between the landing plug and the bottom semiconductor substrate to cause increase of leakage current in the junction region, thereby degrading an electric characteristic of the device.